I often have used UPDATE and INSERT statements during my development. In some complex updates especially when I had to select from other tables I sometimes got strange problems.

I even was able to update the wrong data because my statement was not correctly designed. After this experience I decided to switch to MERGE-statements. Merge Statements are easy to read especially when you use difficult select statements inside.

Here is an example package with an MERGE statement inside. It should show you how such an statement could look like and for me it is a good reminder how to design the code.